Hypertrophic scarring is a condition that sometimes develops after a wound has healed and is recovered with new epithelium. Tissue builds under the new epithelium to a level above the normal skin level, resulting in a scar that is raised. It is also often red, puritic, and painful.
Distinguishing keloids from hypertrophic scars can be difficult. Clinically, keloids can be distinguished from hypertrophic scars in that keloids extend beyond the original wound and rarely regress, whereas hypertrophic scars remain within the confines of the original wound and often spontaneously regress. Both keloids and hypertrophic scars are abnormal wound responses and result from a connective tissue response to trauma, inflammation, surgery, or bums and occasionally seem to occur spontaneously. Both are characterized by the abundant deposition of collagen and glycoprotein.
A therapy that has proven effective in reducing these unwanted characteristics of keloids and hypertrophic scars is silicone sheet therapy. In such therapy, the scar is covered with a sheet of silicone rubber about 140 mil (3.5 mm) thick or, in some reports, about 70 mil (1.75 mm) thick. The scar should be covered for 12 hours per day or more, for a period of at least 8 weeks. If such regimen is followed, existing scars have been found to improve. This treatment has also been shown to be effective as a prophylactic, reducing the incidence of hyprotrophic scars after surgery.
While silicone gel sheeting is now recognized for its effectiveness in preventing the formation of hypertrophic scars and keloids, and for treating existing scars and keloids, the mechanism for its efficacy has remained a mystery and continues to be debated. The medical literature is devoid of an explanation for its effectiveness. Medical investigators have excluded pressure, oxygen tension, temperature and silicone absorption in the skin as possible explanations for its action. Quinn K J, Evans J H, Courtney J M, Gaylor J D, Reid W H (1985), Non-pressure treatment of hypertrophic scars, Burns Incl. Therm. Inj. 12:102-8; Quinn KJ (1987), Silicone gel in scar treatment, Bums Incl. Therm. Inj. S33-40.
The problem with silicone sheet therapy is that it can be difficult to keep the sheet in place over a scar. Silicone sheets that are mildly adhesive have been developed, but these also have problems with staying in place. A preferred time for treatment is while sleeping, but then the sheet can be easily dislodged without the patient's knowledge and therapy is not provided as a result. One reason such a sheet may become dislodged is its substantial thickness, presenting the possibility that such a sheet may be easily caught on a bedsheet or pillow. Silicone tape is often used to hold such a sheet in place, but such tape is relatively expensive compared to conventional medical tapes, the latter being unuseable because they do not stick to silicone gel sheet.
A main aspect of this invention lies in discovering the reasons for the effectiveness of silicone gel sheeting and, based on that discovery, providing a relatively thin film dressing that has critical characteristics identical or similar to those of a silicone gel dressing. Because the dressing of this invention utilizes a film that is thin, flexible and highly conformable, the problems associated with the use of silicone gel sheeting are avoided.
Because of its thinness and flexibility, a dressing of this invention will stay in place much better than currently available silicone dressings. It can be made with less expensive materials and held in place with less expensive tapes. In a preferred embodiment of the invention, the dressing is self-adhesive—that is, it has a coating on one side of a hypoallergenic pressure-sensitive adhesive, thereby increasing patient convenience and providing an added level of stay-in-place performance. The dressing of this invention is also more conformable and less visible or detectable than currently-available dressings intended for the same therapy. Since a dressing should be worn 12 hours or more each day for a period of at least 8 weeks, such advantages are of particular importance to users.
Briefly, the thin film dressing of this invention takes the form of a flexible and anatomically conformable polymeric film having a thickness no greater than about 10 mil (0.254 mm). Such film should have a moisture vapor transmission rate (MVTR) less than that of skin, generally no greater than 15 milligrams per square centimeter per day, and an oxygen transmission rate of at least 300 cubic centimeters per 100 square inches per day. Preferably the MVTR should be 1 to 10 mg/cm2/day and more preferably 4 to 8 mg/cm2/day. As to the oxygen transmission rate, it is preferable that the film have a transmission rate at least 600 cc/100 in2/day, and more preferably at least 2000 cc/100 in2/day.
The thin film is preferably coated on one side with a medical-grade hypoallergenic pressure-sensitive adhesive to facilitate application and retention of the dressing over a wound site. The film and/or its adhesive coating may also be formulated to include a suitable bacteriostatic or microbicidal agent to prevent or reduce skin rashes that might otherwise occur during use of the thin film scar dressing of this invention.
The invention also involves the method of use of such a dressing. Such method is directed to the treatment of dermal wounds for reducing scars and their formation, and involves the step of covering, and preferably adhering, the thin film dressing of this invention to the treatment area. For optimal effectiveness, such a dressing should be worn 12 hours or more each day for a period of at least 8 weeks.